This invention relates to a detector for the measurement of ionizing radiation, preferably γ-radiation and x-rays, comprising a scintillator, emitting light when radiation is partly absorbed, and a light detector, preferably a photo cathode with a photo multiplier optically coupled thereto, the light detector being stabilized by a predefined light source, preferably a light emitting diode (LED), where the length and/or shape of the light pulses of the light source are different from the length and/or shape of the light pulses, emitted by the scintillator, following the absorption of radiation, and an electronic system, stabilizing the whole detector.
In order to increase the measurement accuracy of radiation detectors, it is necessary to either correct the measured data after the measurement has been completed or to stabilize the detector during the actual measurement. Especially in hand-held radio isotope identification devices (RID) and radiation portal monitors (RPM), which are applied for homeland security purposes, it is an advantage to stabilize the detector during the measurement, as this allows a fast and accurate evaluation of the data by people with no education in nuclear physics. RIDs, for example, are mainly used by police or customs, where neither an equipment for the correction of the data after completion of the measurement is available, nor people with a necessary education. In addition and may be most important, measurements in those surroundings have to provide a quick and accurate result.
RIDs, applied for homeland security, are mostly based on γ-spectrometers with scintillation detectors. Such systems must tolerate a wide range of operational conditions, particularly of ambient temperature, detector count rate, and γ-energies of the radiation field. Efficient detector stabilization therefore is essential to maintain energy calibration and resolution if strong and rapid changes of the ambient condition are occurring.
In the prior art, it is known to stabilize a light detector by bringing the light of an LED to the light detector and separating the resulting signals from the signals, induced by nuclear radiation. The shift of the light induced pulses in the light detector then is a measure for the temperature drift of the light detector to be corrected. It is also known to stabilize a scintillator by analyzing the pulse shape of the scintillation output signals.
With the techniques known in the prior art, it is possible to stabilize a radiation detector, namely a RID, to a shift of larger than 2% when the ambient conditions change as described above.